Polyimide resins generally find use in the electronic industry as an insulating material and a protective material for semiconductor devices and liquid crystal display devices because of their outstanding characteristic properties, such as high mechanical strength, high heat resistance, good electrical insulation, and good solvent resistance. Their recent prospective application area is optical communications, particularly optical waveguide.
The rapid development in this area needs materials with much more improved properties than before. Such materials must have not only good heat and solvent resistance but also various properties suitable for specific uses.
Among important properties is high transparency. High transparency is realized with a polyimide which is produced by polycondensation reaction between an alicyclic tetracarboxylic dianhydride and an aromatic diamine and ensuing imidization of the resulting polyimide precursor. The thus obtained polyimide has been reported to have high transparency with a comparatively low level of discoloration. (See Patent Documents 1 and 2.)
An example of the alicyclic tetracarboxylic dianhydride is 1,2,3,4-cyclobutanetetracarbocylic acid-1,3:2,4-dianhydride. It can be synthesized by combination of the following two schemes.                Synthesis from dimethyl fumarate (A) into trans, trans, trans-1,2,3,4-cyclobutanetetracarboxylic acid (D). (See Non-Patent Document 1.)        Synthesis from trans, trans, trans-1,2,3,4-cyclobutanetetracarboxylic acid (D) into 1,2,3,4-cyclobutanetetracarboxylic acid-1,3:2,4-dianhydride (E). (See Non-Patent Document 2.)        

The process disclosed in Non-Patent Document 1 suffers the following disadvantages.    (1) The first step (for photoreaction) takes a very long time (one to five days).    (2) The second step (for isomerization) needs a high temperature (300° C.).    (3) The alternative second step (for isomerization) needs a large amount of base (6 equivalents) and is very poor in yields.    (4) The third step (for hydrolysis) needs concentrated hydrochloric acid, with nothing disclosed about yields.
The process disclosed in Non-Patent Document 2 suffers the disadvantage of precipitating 1,2,3,4-cyclobutanetetracarboxylic acid-1,3:2,4-dianhydride, which is the object product (E), in the form of colored solid. Moreover, it is unclear whether the disclosed process actually gives the cyclic compound as desired because the object product was examined for chemical structure only by IR but not by single-crystal X-ray diffractometry (for absolute structure).
In addition, there is no known compound composed of 1,2,3,4-cyclobutanetetracarboxylic acid-1,3:2,4-dianhydride and alkyl groups attached to the cyclobutane ring.
Patent Document 1:                JP-A 60-188427        
Patent Document 2:                JP-A 58-208322        
Non-Patent Document 1:                J. Am. Chem. Soc., 83, 2725-8 (1961), vol. 83, pp. 2725-2728.        
Non-Patent Document 2:                J. Org. Chem., 33(3), 1018-1021 (1968).        